A motor vehicle may be fitted with an Exhaust Gas Recirculation (EGR) system configured to recirculate a portion of the exhaust gases of an engine back to an inlet of the engine. Replacing a portion of the oxygen rich inlet air with burnt exhaust gases reduces the proportion of the contents of each cylinder of the engine which are available for combustion. This results in a lower heat release and lower peak cylinder temperature and thereby reduces the formation of NOx.
In order for the engine to continue operating efficiently, it is desirable for the reintroduced EGR gases to be mixed homogenously with the inlet air. The engine usage, load, and range of speed determine the amount of EGR requested for the engine. In general, the EGR will mix with the fresh air more readily at some engine operating points than others. An EGR diffuser may be provided within the inlet air duct to facilitate mixing of the EGR gases and inlet air. For example, an EGR diffuser may utilize static features such as plates and hole patterns to dissipate and mix the EGR into the intake system of the engine. The geometry of the EGR diffuser may be defined to provide homogenous mixing of EGR gases and inlet air at a specific operating condition of the vehicle.
However the inventors herein have recognized potential issues with such diffusers. As an example, the above-discussed static features may cause the engine to work harder, resulting in pumping losses. As another example, they may deliver a less than desired EGR mass into the cylinders. This may be due to the request for a higher pressure differential required at the EGR diffuser to jet the EGR into the air stream. The issue may be exacerbated at high engine speeds where higher intake volumes can further raise the pressure differential required for EGR delivery. As such, this affects engine emissions and fuel economy.